The control of animal parasites is one of the oldest and most important problems of the animal husbandry industry. Many types of parasites afflict virtually all species of animals. Most animals are afflicated by free-flying parasites such as flies, crawling ectoparasites such as lice and mites, burrowing parasites such as bots and grubs, and by microscopic endoparasites such as coccidia, as well as by larger endoparasites such as worms. Thus, the control of parasites even in a single host species is a complex and many-sided problem.
The insect and acarina parasites which consume living tissues of a host animal are particularly harmful. The group includes parasites of all the economic animals, including ruminant and monogastric mammals and poultry, and of companion animals such as dogs as well.
Many methods of control of such parasites have been tried. The screwworm has been practically eradicated in Florida by the release of great numbers of sterile male blowflies. The method obviously is applicable only to an easily isolated area. The free-flying insects are usually controlled by routine methods such as air-dispersed and contact insecticides and fly traps. The skin-inhabiting crawling parasites are usually controlled by dipping, drenching, or spraying the animals with appropriate parasiticides.
Some progress has been made in the systemic control of some parasites, particularly those which burrow in or migrate through the host animal. Systemic control of animal parasites is accomplished by absorbing a parasiticide in the bloodstream or other tissues of the host animal. Parasites which eat or come into contact with the parasiticide-containing tissue are killed, either by ingestion or contact. A few phosphate, phophoramidate, and phosphorothioate insecticides and acaricides have been found to be sufficiently nontoxic to be used systemically in animals.
Recently, the field of benzimidazole chemistry has been extremely active. A great many patents and publications have appeared disclosing a variety of substituted benzimidazoles, some of which have insecticidal and acaricidal activity.
For example, Belgian Pat. No. 766,870, Derwent Index No. 72165S-C, teaches a group of acaricidal benzimidazoles characterized by 1-carboxylate and 2-chlorofluoroalkyl substituents and a variety of substituents, including halo, nitro, and trifluoromethyl, on the benzene ring.
Newbold et al., U.S. Pat. No. 3,542,923, discloses an insecticidal method making use of benzimidazoles having no 1-substituent or a 1-carboxylate substituent, a 2-perfluoroalkyl substituent, and as many as four benzene ring substituents chosen from among a large group of substituents including nitro, halo, alkyl, carboxy, and so forth.
British Pat. No. 1,122,988 teaches insecticidal and acaricidal benzimidazoles of structures notable for the extremely wide variety of the benzene ring substituents, of which the compounds can have as many as four. The 2-substituents of the components are perfluoroalkyl, and the 1-substituent, if present, is alkyl or aryl.
British Pat. Nos. 1,087,561 and 1,144,620 provide further disclosure of insecticidal 2-perfluoroalkyl benzimedazoles.
French Pat. No. 1,430,139 adds another group of insecticidal, acaricidal, and nematocidal benzimidazoles bearing as many as four benzene ring substituents chosen from the group including nitro, chloro, and cyano, among others, and a 2-haloalkyl substituent.
British Pat. No. 1,113,999 discloses a group of 1-thiocarbamoylbenzimidazoles which are insecticides active against pests such as mustard beetles, aphids, and mosquitoes.
South African Pat. No. 69.02813 teaches the biological activity of a family of benzimidazoles including compounds with 1-carboxylate and 1-sulfonyl substituents. The compounds are insecticides and acaricides.
Holan et al., U.S. Pat. No. 3,448,115, discloses a family of substituted benzimidazoles characterized by a 2-dichlorofluoromethyl or chlorodifluoromethyl substituent. The compounds of the patent are stated to be anthelmintics and herbicides.
Hannah et al., U.S. Pat. No. 3,749,734, discloses a group of 1 -cyanobenzimidazoles having chlorine atoms on the phenyl ring which are said to be anthelmintics and ectoparasiticides.